A variety of power supplies exist to facilitate recharging of portable electronic devices. Such power supplies typically receive alternating current (AC) power from a wall socket or other AC power source and supply direct current (DC) power for use by the portable electronic devices, such as smartphones, tablet computers, portable multi-media device, laptop computers, portable gaming systems, or other portable electronic devices.
Some power supplies include multiple output ports, such as Universal Serial Bus (USB) ports, to enable the power supply to charge multiple load devices simultaneously (e.g., smartphone and tablet computer, smartphone and portable gaming device, tablet computer and portable multi-media device, and so forth). Such multi-port supplies are either designed to support the maximum amount of power that may be cumulatively requested by the load devices or, when not so designed, may become unstable under overload conditions. Designing the power supply for maximum possible aggregate load adds unnecessary size and expense, especially where the power supply may not be asked often to supply maximum power to all output ports. On the other hand, failing to design the power supply to handle maximum load may cause one or more of the output voltages to enter a loop in which the output voltage repeatedly drops to zero and then attempts to recover to full value so long as the cumulative power demand from the load devices is in excess of the aggregate power available from the supply. The supply of such a looping output voltage may cause a connected load device to repeatedly reboot or otherwise act erratically, and could ultimately damage the device and/or cause a bad consumer experience.
One proposal for managing power supplied to the two output ports of a dual output power converter when an overload condition is present is described in U.S. Pat. No. 7,781,908 B2. According to this proposal, one output port is identified as being a high power output and the other output port is identified as being a low power output. During operation of the power converter, the output power delivered to the high power output is monitored. If the power delivered to the high power output remains below a threshold for a period of time, the low power output is activated. If the power delivered to the high power output later exceeds the threshold for a period of time, an electronic circuit powers down the low power output (i.e., turns off or deactivates the low power output) in order to keep the total output power below the rated power for the power converter. After a period of time, the power drawn by the high power output is checked again and, if the drawn power has dropped below the threshold, the low power output may be reactivated. If the power drawn by the high power output exceeds the rated power for the power converter, both the high power output and the low power output are turned off and the converter must be unplugged from its power source.
The output power management approach disclosed in U.S. Pat. No. 7,781,908 B2 provides a binary approach to power management, whereby power ceases to be delivered to at least the low power output when the power converter is in an over power or overload condition. Thus, if a portable electronic device is coupled to the low power output port when an overload condition arises, the portable electronic device may reboot or otherwise act erratically in response to a loss of source power, thereby causing a bad consumer experience.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated alone or relative to other elements or the elements may be shown in block diagram form to help improve the understanding of the various exemplary embodiments described herein.